The labeling operation of containers in high speed automatic labeling machines sets out the problem of the correct positioning of the label. Such machines usually comprise turntables, on which a plurality of pans is mounted, which are intended to support and handle the containers to be labeled, together with jacks engaging the container upper end in order to hold it in an upright position on the pan. Such pans are motor-driven, so as to allow the rotation thereof and of the containers they support around the vertical axis thereof. This operation serves to the label application, which label will thus wrap around the container side surface during the rotation thereof.
In a machine as the one described herein, which operates at a high speed, the container angular orientation according to a preset pattern is critical for a smooth operation of the machine.
In the conventional plants, the container correct orientation is achieved by a timing of a mechanical type which, however, often turns out to be not very reliable.
In labeling machines for glass containers, systems have been proposed wherein one or more cameras are positioned along the path of the carrousel in order to read an indentation or other marks such as wrinkles or dots that are present on a bottom area of the container. These systems also comprise a computing and control unit that elaborates the images taken by the one or more cameras, makes a comparison between such images and a reference image or a calibration graph and finally controls the rotational position of the containers on the supporting pans, so that the containers are all oriented the same way.
One critical issue in these systems is the reliability of identification of such indentation or marks present on the containers. Errors in the identification of such marks would result in an erroneous re-positioning of the container and thus in an unreliable labeling operation.